Treatment of Sulfidic Wastewater Using Iron Salts

Abstract

Sulfides are often found to be present in the effluents generated from some chemical and petrochemical industries as well as from tanneries. Beyond a certain permissible limit, sulfides are generally toxic to living bodies. In the present work, solution of sodium sulfide was first mixed with \(\hbox {Fe}^{+2}/\hbox {Fe}^{+3}\) salt solutions in different ratios which resulted in precipitation of sulfide from the solution. This was followed by aeration of the residual solution. The maximum sulfide removal efficiency of the \(\hbox {Fe}^{+2}/\hbox {Fe}^{+3}\) treatment was approximately 70 %. However, upon aeration, the residual sulfide was eventually removed. The precipitate formed was characterized as ferrous sulfide, applying scanning electron microscopy, energy-dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy and X-ray power diffraction. The role of sulfide concentration, \(\hbox {Fe}^{+2}/\hbox {Fe}^{+3}\) ratio and temperature on the kinetics of sulfide removal from the aqueous solution was investigated. Effect of air flow rate during aeration of remaining sulfide was also investigated. The rate equation and activation energy for the precipitation reaction were calculated from the experimental results. The results of this study hold promise for effective treatment of sulfidic wastewater in chemical and allied industries.